1. Field of Invention
The present invention relates to telecommunication network and, more particularly, to managing presence information on a network.
2. Description of Related Art
In general, a presence server on a packet-switched network can maintain records indicating the presence status of various users (or, equivalently, stations), that is, whether the users have IP addresses and are online and therefore available to engage in packet-data communications. Further, the presence server can be arranged to notify certain users when changes occur in the presence state of certain other users.
For instance, under the well-known Session Initiation Protocol (SIP), when a user acquires an IP address, it can automatically send a SIP REGISTER message to the presence server, and the presence server would record that the user is online. Typically, the REGISTER message will carry with it an expiration time, which indicates how long the registration would remain active. To maintain the registration, the user would send a new REGISTER message before the last one expires.
Applying “presence extensions” to SIP, a user can then send a SIP SUBSCRIBE message to the presence server, asking the presence server to notify it when one or more other users goes online or offline. When one of the other users goes online or offline, the presence server would then send a SIP NOTIFY message to the user who subscribed to be notified, telling the user of the change in presence status.
This process can be used to facilitate upkeep of “buddy lists” on client stations, to enable group communications such as instant messaging or push-to-talk communication for instance. By way of example, each client station that is a member of a group (or is used by a member of a group) may subscribe to the presence server to be notified when any member of the group goes online or offline. Using the process described above, the presence server would then notify each subscribing member when a change in presence status occurs with respect to another member of the group. Upon receipt of a NOTIFY message indicating a change in presence status of a group member, a client station can then update its buddy list. A user of the client station can thereby know which group members are available at any given time to engage in group communications.